`sourceUri` needs to be passed into `processInlineStyles` styles as well.  You need to write a test to make sure images are being resolved properly.  For example, passing in `http://test.invalid` as the `sourceUri` for the below style should turn the image path into `http://test.invalid/images/Earth_Station.png`, but right now it doesn't.

```
<Style>
  <IconStyle>
    <Icon>
      <href>images/Earth_Station.png</href>
    </Icon>
  </IconStyle>
</Style>
```